US 3833409 A
A printing ribbon for non-impact electrical printing consists of an insulating base film, having a microcavernous surface formed by microscopic crags having deep rough and irregular pits or valleys between them with fine conductive printing particles loosely retained on and in the surface.
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Description (OCR text may contain errors)
United vStates Patent BEFORE BRU Peshin Sept. 3, 1974 DONOR SHEET FOR PULSED ELECTRICAL [5 6] References Cited PRINTING UNITED STATES PATENTS  Inventor: John Peshin, Westwood, Mass. 3,550,153 12/1970 Haeberle et a1. 346/74  A gne T e Carters k Company, 3,617,328 11/1971 Newman 117/29 Cambndge Mass Primary Examiner-Cameron K. Weiffenbach  Filed: Jan. 7, 1972 Attorney, Agent, or Firm-Kenway & Jenney 21 A LN 21 194 1 pp 57 ABSTRACT A printing ribbon for non-impact electrical printing  525 7 7 consists of an insulating base film, having a microcav-  Int Cl 844! 1/16 B44d 1/18 ernous surface formed by microscopic crags having Fie'ld 5 74 SB 74 so deep, rough and irregular pits or valleys between them with fine conductive printing particles loosely retained on and in the surface.
5 Claims, 3 Drawing Figures ISATENTEDSEP 31974 sum 2 or 2 FIG. 3
BACKGROUND THE INVENTION This invention relates to printing ribbons suitable for use in the non-impact printing (NIP) system described by Haeberle et al in US. Pat. No. 3,550,153 dated Dec. 22, 1970.
The patent of Haeberle et al describes method and apparatus for printing an image upon a recipient sheet by disposing closely adjacent to that sheet a donor sheet which carries mobile electrically conductive printing particles in or on a high resistance medium, and then applying through the thickness of the two sheets a shaped electrical field pulse of short duration corresponding in outline to the image to be printed. In this method the pulse is effective to establish a current flow which causes the printing particles to become charged and then transferred from the donor sheet to the recipient sheet.
BRIEF DESCRIPTION The object of this invention is to provide a printing ribbon, or donor sheet, having a high density of readily removable and transferable printing material such that images of good tone and contrast may be produced. These characteristics are provided without the problems of dusting and smudging, and problems associated with the handling and utilization of dark colored, finely divided materials, such as the dry toner employed in the numerous electrostatic printing processes.
In brief this invention provides a sheet material which is relatively clean to handle and not given to smudging or dusting, yet which carries loosely a relatively large quantity of finely divided printing particles that may be readily transferred by the electrical pulses employed in the printing step.
It is a requisite to the NIP system described by Haeberle et al that the printing ribbon or donor sheet have a relatively high electrical resistivity, particularly in the lateral directions, so as to preserve the shaped character of the electrical field pulse applied for printing. A conductive sheet would destroy the integrity of the field shape in the region remote from the shaped electrode, such as between the sheet and a ground plate. The printing ribbon of this invention accordingly employs a sheet of relatively insulating material such as paper, polyethylene terphthalate, polypropylene or the like. To this is applied a base coat which develops a rough outer surface of microscopic crags which present deep, rough and irregular pits or valleys capable of retaining the printing particles. This rough surface provides not only a larger area than would a smooth surface, by a factor of about two to five times (based on squaring the linear measurements of the actual surface outline and of its projection, made from photomicrographs of cross sections of the sheet) but also cavities in the surface in which the particle may lie captive. The printing particles are loosely retained on the surface and inv the pits or valleys, essentially by frictional and surface forces.
The base coat is conveniently formed form a mixture of an insulating filler material of particle size between about 5 and 175 microns and an insulating resin binder solution of high solvent content, e.g. over 50% by volume on the total mixture, and low resin content, e.g.
5-40% on total solids. The base coat is applied to a thickness suitable to accomodate the largest filler particles in the final coating and is then dried, whereupon the evaporation of solvent leaves the above described rough microscopically craggy structure.
To the base coat is then applied the printing particles, preferably by forming a suspension of the particles, e. g. activated charcoal 0.25-15 microns in size in a nonsolvent for the base coating, to cover the base coatingcompletely. After the suspension has dried, the surface is gently brushed to remove excess printing particles that lie above the general top surface level of the base coating and to distribute the particles in irregular piles scattered over the surface of the base coat. The printing particles not only fill the pits of the micro cavernous base coat but lie all over the surface in loose irregular piles.
A printing sheet as thus formed is well suited for use in the process described by I-Iaeberle et al.
DESCRIPTION OF FIGURES The nature of the printing sheet of this invention is shown in the drawing in which:
FIG. 1 is a visualization, based on photomicrographs, of a cross section in elevation of the sheet of this invention at a magnification of about 1,000x;
FIG. 2 is a visualized enlargement of the circular area of FIG. 1 to a magnification of about 10,000x; and
FIG. 3 is a photomicrograph taken by a scanning electron microscope at 1,000x magnification and 45 inclination, of the top surface of the base coat prior to the incorporation of printing particles.
As shown in FIG. 1 the printing ribbon consists of a thin film 10 having on one surface a rough coating 12 which provides an outer surface of microscopically deep, rough and irregular contours presenting microscopic pits or valleys in which the printing particles 14 are retained. Typically these pits or valleys are about 10-50 microns in depth and across. In FIG. 1 the nature of the coating is illustrated in some detail to show filler particles 15 in the resinous binder 16, the particles serving to define crags which impart the rough and irregular shaped to the surface. The nature of the outer particulate surface in the final product is shown in the right hand part of FIG. 1 After Brushing, and a visualized enlargement thereof is shown in FIG. 2. The printing particles are of the order of 12 microns or smaller and lie loosely on the coating, filling the pits or valleys and also scattered over the entire surface in irregular piles of more or less loose particles which remain in place apparently by surface'forces. The presence of the scattered piles developed after brushing is believed to be important in the printing operation in that peaks or pinnacles are presented where particles would be most readily charged up upon application of electrical field pulse, and then dislodged and caused to move in the field. The field forces tend to concentrate at the peaks or pinnacles and the effect of the field is greatest in these concentrated regions.
The following example sets forth in detail the procedure for preparing a printing ribbon in accordance with this invention.
EXAMPLE I Estane 57l5 B. F. Goodrich 15 grams EXAMPLE I-Continued Silica sand, -30 microns, Min-U-Sil Pennsylvania Glass Sand Corp.
Methyl Ethyl Ketone (MEK) 25 grams 60 grams opment of the above described microcavemous surface. The sand particles develop crags with peaks correspondingto the diameter of the larger particles, and the crevices between these crags may have a coating thickness only the thickness of residual resin, or of the thickness of smaller particles. In this example the peak thickness of the coating will be up to 50 microns. To this is applied a carbon coating prepared by dispersing activated charcoal (Nuchar CN, West Virginia Pulp and Paper Co.) in methanol or ethanol in the weight ratio of 15 carbon: 85 solvent. The dispersion is first ball milled to reduce the particles to 12 microns or less. The carbon dispersion is then coated onto the previously coated film in theamount of 10 ouncesper 3,000 square feet and dried.
The dried coated film is illustrated in FIG. 1 on the left hand side Before Brushing.
The final step in the processing is to brush the coating. This may be accomplished with a rotary brush of 1 inch long bristles of approximately 50 denier orless. Brushing is carried out to remove the top surface of the particles and to cause a distribution in the nature of scattered piles as illustrated at the right hand side of FIG. 1 After Brushing and in FIG. 2. Brushing should be carried out to achieve the effect illustrated but should not be carried out to the point of exposing the underlying rough surface. An overall coating depth to a minimum of about 10 microns is normal for this example.
The sheet thus formed may be used directly in nonimpact electrical printing in the manner described by Haeberle et al. Pulses of the order of 1-2 microseconds and 800 volts will print distinct characters.
The base film and filled resin coating should be of relatively high resistivity such that the configuration of the electrical field pulse applied for printing is not disrupted or equalized by the interposition of an electrically conductive layer. Accordingly the'base film can be any of a number of synthetic organic resins as may the'surface coating, and the filler particles should be generally less than 50 microns in mean diameter, and preferably rough and irregular in shape. These particles are generally responsible for the rough and irregular nature of the surface and'should be selected so as to provide the microcavemous effect .described.
The printing particles should be relatively highly conductive in order to acquire the necessary electrical charge for printing, should be loosely applied, but not in intimate electrical contact, so that the high transverse resistivity of the sheet as a whole is preserved. Suitable materials, in addition to charcoal, that may be employed include:
Nigoa Cul CdS PbO co t nu C0 0. CuS PbO C%O CuO U0, Ni ZrN Cu,0
As illustrated and described above the printing sheet of this invention features a rough and irregular base surface of high lateral resistivity on and in which lie conductive particles of print material. The base surface serves to retain the print materialwithin its surface irregularities, that is to say in the pits and crevices; and, being highly resistant laterally, it does not cause equalization of a shaped pulse. The particles on the other hand, readily acquire a charge sufficient to move them from the base surface under the field of the printing pulse, and in accordance with the shape of that field.
It is accordingly contemplated that the base surface, underlying and retaining the print particles may be any insulating resin with the filler particles geometrically arranged to present the rough microscopically craggy surface described, having an overall high lateral D.C. resistivity, with particles of low resistivity brushed over and in the crevices. In this connection it is noted that the print particles listed above include not only highly conductive materials such as carbon,.but also several semi-conductor materials such as CdS.
A criterion of the surface of the print ribbon or donor sheet of this invention is that the print particle carrying surface have alateral D.C. resistivity of at least 10 ohms per square.
Having thus disclosed this invention and described in detail the preferred embodiment, we desire to secure and claim by Letters Patent thefollowing:
l. A donor sheet useful in pulsed electrical printing, comprising a base sheet having a microcavemous surface with pits-or valleys of about 10-50 microns across and 10-50 microns deep, and print particles having a conductivity at least that of a semi-conductor loosely lying on the surface in said pits or valleys, said particles being about 0.25-l5 microns across and present in quantity sufficient to effect printing by transfer of particles to an adjacent sheet upon imposition of an electrical pulse of about 800 volts for two microseconds, said sheet having a lateral surface D.C. resistivity of at least I0 ohms per square.
2. A donor sheet as defined by claim 1 wherein the microcavemous surface of the base sheet presents a total surface at least two times its projected area which is based on squaring the linear measurements of the actual surface outline and of its projection.
3. A donor sheet as defined by claim 1 wherein the base sheet surface comprises particles of filler 5-175 microns across, embedded in a synthetic organic insulatin resin, said resin being between 5 and 40% by weigit of the total resin plus filler.
4. The method of making a donor sheet suitablefor pulsed electrical printing comprising the steps of:
mixing coarse particles of filler 5-175 microns across in a solution of an organic insulating resin having a solvent content over 50% by volume and a resin tc tl)lntent of 540% by weight based on resin plus coating said mixture onto a base sheet,
drying said coating, thereby forming a microcavemous surface coating on said sheet with pits or valleys of about 10-50 microns across and l050 microns deep, and
applying loose print particles to the dried coating, said particles having a conductivity at least that of a semiconductor, and said particles being of size between about 0.25 and 15 microns.
5. The method defined by claim 4 wherein the print particles are brushed on the coating.